SAW devices for spread spectrum applications

Surface acoustic wave (SAW) filters are small, rugged, and crystal stable. They can be fabricated with high reproducibility. In the 80s they replaced the LC filters in TV sets and more than one hundred million SAW TV IF filters are fabricated each year. SAW filters play a key role in the rapidly growing market of mobile communication systems. They enable advanced system concepts and contribute to the reduction of the size of the handhelds. They are used in the IF and RF stage as well. SAW filters are also used for channel filtering in narrowband code division multiple access (CDMA) mobile communication systems. A new application for SAW filters might be as analog correlators in broadband CDMA communication systems. Compared to digital signal processors (DSP) they exhibit a relative low power consumption and can perform real-time correlation of signals with absolute bandwidths up to a few hundred MHz easily. One drawback is the limitation of the integration time length of SAW devices, which is typically less than 16 μs due to the size of the substrate wafers (typically 3"). Requirements on SAW devices as analog correlators are stringent with respect to insertion loss, stop-band attenuation, amplitude ripple and phase nonlinearity. To fulfil these requirements efficient CAD tools for the simulation and synthesis of SAW devices are a prerequisite